The present invention relates to floor polishers or burnishers; and more particularly, it relates to so-called high speed burnishers. As used here, "high speed" refers to rotary burnishing machines wherein the floor-contacting pad is rotated at an angular velocity greater than 1,000 revolutions per minute. Typically, such machines may operate at speeds up to 1,800 or 2,000 RPM.
Modern floor burnishers operating at high speeds of the range with which the present invention is concerned have a number of problems. Typically, the polishing pad is made of synthetic or natural fiber wherein the fibers are very loosely woven together. Adhesive or physical interconnection may be used to connect the fibers, but there is nevertheless a tendency for the cirumference of the pad to creep or "grow" during use. This problem is even more pronounced at higher operating speeds such as 2,000 RPM; and the result is a thinning of the pad resulting in a greatly accelerated wear and corresponding reduced life of the pad.
There are at least two different types of burnishing action in high speed machines (both of which experience the problem of pad expansion mentioned above). In one type of burnisher, the axis of rotation of the pad is slightly off the vertical so that the pad contacts the floor at a slight incline. Pressure is greater at the lowest point of the pad, which is on the periphery at one point, but the diametrically opposite point of the pad has little or no contact with the floor. Burnishing is achieved in the area of forced contact, and the downward force on the pad is chiefly provided by the weight of the machine. Another type of burnisher relies on full circumferential contact between the pad and floor and the downward force is substantially uniform in the entire contact area which is annular in shape. In this type of machine, contact is achieved because the pad is highly porous and the high rotary speed evacuates air from the pad under centrifugal force. The air is forced outwardly thereby evacuating the pad, and atmospheric pressure acts uniformly downwardly on the pad driver bringing the entire pad driver (which ideally rotates about a true vertical axis) downward forcing the pad into full circumferential engagement with the floor. This type of machine (which we refer to here as a "full contact" type) is believed to be more advantageous because the maximum load current drawn from a conventional wall outlet is limited under normal use conditions and because a high luster can be achieved.
In the latter type of machine, however, the weight of the machine can actually be a disadvantage unless some special provision such as a center caster is incorporated into the machine because there is a tendency to cause the outer edges of the pad to curl up and lose their ability to burnish effectively. A rigid back plate does not solve this problem satisfactorily because then the pad drive cannot follow variations in floor contour. Flexibility to the driver assembly is desirable.
Still another problem associated with high speed floor burnishers is that operation of the burnisher generates dust which, if not collected, rapidly spreads thoughout the area being conditioned, and the dust quickly will cover desks or other furniture in the area.